Subsequent to inserting an X-ray film cassette into the holder in the cassette-changing position, the cassette must be centered in the direction of the X and Y axes. This centering of the cassette is encumbered with certain difficulties, due to the fact that cassettes of mutually different sizes are required for photographing different parts of the body. These cassettes normally occur in at least nine different standard dimensions, both in centimetres and in imperial inches.
The cassettes are normally centered through the agency of separate dogging or centering means, which are normally arranged in pairs, i.e. two dogging means are arranged to centre the cassette in the X-direction and two in the Y-direction.
The dogging means are normally moved by a link-mechanism forming part of a separate auxiliary operating device carried by the holder.
Great Britian patent application No. 1 358 660 (Philips Electronic) describes a cassette holder which can be swung relative to a box and which is provided with one such auxiliary device in the form of a handle.
Other similar solutions with corresponding disadvantages are described in, for example, U.S. Pat. No. 4,128,767 (Stodberg et al), European patent application No. 0068212 (Siemens) and U.S. Pat. No. 4,246,488 (Hura).
Japan patent application No. 58-57127 (Seisakusho et al) describes a different arrangement, in which a cassette is centered only in the X-direction or in the Y-direction when inserted in the actual holder.